Before 1943, the British and American fleets escorting the transport fleet in the Atlantic Ocean were often attacked by German submarines, and a large number of military materials, including tanks, artillery, gasoline, guns and ammunition, sank to the bottom of the sea before being delivered to the frontline soldiers. At that time, Britain and the United States could not send a large number of escort ships. What should we do?

The US Navy general consulted several mathematicians, and mathematicians found that the fleet and enemy submarines may or may not meet. This is a random event with certain rules. The smaller the fleet size of a certain number of ships (such as 100 ships), the larger the order quantity (such as 20 ships at a time, there must be 5 orders); The more teams there are, the greater the probability of meeting the enemy. For example, when five students come home from school, the teacher can find 1 student and go to any one. But if these five students are all in one of them, the teacher has to find a few to find them, and the possibility of finding them at one time is only 20%.

The US Navy accepted the mathematician's advice and ordered the fleet to assemble in the designated sea area, then collectively pass through the dangerous sea area, and then separately sail to the scheduled port. In this way, the sinking probability is reduced from 25% to 1%, which greatly reduces the loss and ensures the timely supply of materials.